The present invention relates to processes for the hydroconversion of heavy hydrocarbonaceous fractions of petroleum. In particular, it relates to a close-coupled, two-stage process for the hydrothermal and hydrocatalytic conversion of petroleum residua having improved effectiveness for demetalation and inhibition of adverse coke formation in the first stage.
Increasingly, petroleum refiners find a need to make use of heavier or poorer quality crude feedstocks in their processing. As that need increases, the need also grows to process the fractions of those poorer feedstocks boiling at elevated temperatures, particularly those temperatures above 1000.degree. F., and containing increasingly high levels of undesirable metals, sulfur, and coke-forming precursors. These contaminants significantly interfere with the hydroprocessing of these heavier fractions by ordinary hydroprocessing means. These contaminants are widely present in petroleum crude oils and other heavy petroleum hydrocarbon streams, such as petroleum hydrocarbon residua and hydrocarbon streams derived from coal processing and atmospheric or vacuum distillations. The most common metal contaminants found in these hydrocarbon fractions include nickel, vanadium, and iron. The various metals deposit themselves on hydrocracking catalysts, tending to poison or deactivate those catalysts. Additionally, metals and asphaltenes and coke precursors can cause interstitial plugging of catalyst beds and reduce catalyst life. Moreover, asphaltenes also tend to reduce the susceptibility of hydrocarbons to desulfurization processes. Such deactivated or plugged catalyst beds are subject to premature replacement.
Additionally, in two-stage processes similar to this, thermal hydrotreating reactors are very susceptible to the adverse formation of coke on various components of the reactor. In particular, it has been found that coke builds up significantly on the walls of the reactor and that this coke build-up, if unchecked, will eventually cause the reactor to plug up, thereby necessitating timeconsuming and expensive rehabilitation. It is the intention of the present invention to overcome these problems by using a two-stage, close-coupled process, wherein the action of a first-stage hydrothermal reactor induces demetalation and some hydroconversion and suppresses adverse coke formation within the reactor, particularly on the reactor walls. The treated effluent from the first stage is then passed, close-coupled to a second-stage hydrocatalytic reactor where it is hydroprocessed to produce high yields of transportation fuel.